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| 2.76 vs 2.9 rear in Feather Dusters https://slantsix.org/forum/viewtopic.php?t=58799 |
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| Author: | Louise76 [ Tue Dec 08, 2015 4:28 pm ] |
| Post subject: | 2.76 vs 2.9 rear in Feather Dusters |
Am I missing something here? I thought the super-high gas mpg Feather Dusters had 2.9 rear ends with the /6 & OD trans. Is that right? If everything else with /6 & 904 trans had 2.76 rears, why didn't Chrysler use 2.76 for economy of mpg? Was the 2.76 too much for the OD? 
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| Author: | DusterIdiot [ Tue Dec 08, 2015 6:11 pm ] |
| Post subject: | Yes... |
It drives the rpm band down so bad the Holley can't enter the mains.... Low ratio rear gears don't really mean mileage unless the rpm band at cruise matches the cams ability to provide peak torque....1500 rpm is a bit below when the mains on most carburators would engage.... literally the final ratio on the automatic car is 2.76...the final ratio on the feather duster is 2.15 (and OD wasn't so nice at 55 mph, vs. 65-75 mph).... Also the 2.94 matches 1st gear pretty well for a nice "leaving ratio" for the A-833 OD and the A-230 that first was installed in the versions produced in the first month or so of the 1976 production run.... 2.76 is pretty tried and true in the automatic cars...but is not as peppy as with the 2.94 (which was a typical ratio in the early-mid-60's behind automatics)... There used to be a couple of nice spread sheets on one of the mopar boards that will help calculate your rpm/speed after inputting the tire size and rear axle ratio....it will give you a real good idea of where the drivetrain performs so you can dial in your cam choice, your engine build, your carb mods, or your timin curve... |
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| Author: | SlantSixDan [ Tue Dec 08, 2015 7:17 pm ] |
| Post subject: | |
With automatic transmission, you have torque multiplication from torque converter, so can get away with higher (lower numerically) rear axle ratio. With manual transmission, you don't, so you need lower (higher numerically) rear axle ratio or the car will be an unsafe slug, unable to get out of its own way from a stop. |
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| Author: | ProCycle [ Tue Dec 08, 2015 7:40 pm ] |
| Post subject: | |
2.76 ~ 2.94 There's only about 6% difference between them. That's maybe 100 rpm at freeway speed. |
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| Author: | Louise76 [ Tue Dec 08, 2015 9:41 pm ] |
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"...unable to get out of its own way from a stop." Ah-ha! Thanks for the schooling, guys. P |
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| Author: | SlantSixDan [ Tue Dec 08, 2015 11:25 pm ] |
| Post subject: | |
Quote: 2.76 ~ 2.94
The straw that broke the camel's back weighed only as much as a straw.
There's only about 6% difference between them. |
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| Author: | DusterIdiot [ Wed Dec 09, 2015 6:13 am ] |
| Post subject: | Lol... |
Quote: The straw that broke the camel's back weighed only as much as a straw.
I have driven this generation duster for a while and even have had the experience of swapping rear ends in it with differing ratios in the same car and can say that 2.76 as a rear ratio in a manual car with stock 225, is a clutch burning experience to get the thing motivated....at top end to get the 1945 into the mains the average rate of speed on the highway had to be about 70-75 mph.... As Dan said that 6% is enough to put the platform out of the sweet spot... |
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| Author: | Joshie225 [ Wed Dec 09, 2015 8:35 am ] |
| Post subject: | |
I hated the 2.76 gears in my '67 Valiant with the 3 speed, but that was the rear end I had at that moment to replaced the failed 3.23 geared 7 1/4. Later that was swapped for a 3.21 geared 8 1/4 and life was much better! |
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| Author: | bob fisher [ Tue Dec 15, 2015 5:27 am ] |
| Post subject: | driving behavior,od manuals and high axle gears. |
high sages- participated in this discussion years ago on this original forum and before in the slantsix mag. have a 76 feather 6 with manual od and the 2.94 axle and had a 77 aspen wagon 6 with manual od and 3.23 axle. plus lots of miles on both. strangely the wagon was more flexible in various driving situations and got better mpg, despite a 2 barrel carb and more weight- on many jersey to fla runs it would get 29 and even around town it would get 22. but the feather which was more sluggish around town got only 20 in town and usually bested 31 32 on fla runs. take off was noticeably slower on the feather which led to me being cussed almost as much as takeoffs in my present volvo 240 wagon( 5speed .80 od , 3.31 axle and a slant 4). as our doctor tells us all these combos depend on the type of driving you do. driving a slug among todays road warriors would be dangerous like flying a spad against mig 15s. in a or f bodies with 6 best all around combo would be the 3.23 axle and manual od. you could get by with the 2.94 but it wouldnt be as easy to drive , definitely not a 2.76. remember the od has a higher top gear(.73) which gives you the mpg. most of these 4 cyl. tanks today have a lower od gear(.80-.90). our doctor once said a 2.76 axle with a 318 would be a an interesting combo. i would go further and would like to see a 318 in an f or a body with the 2.45 axle and manual trans. highest rear gear i saw was 2.26 but that was in automatic polaras and newports used by turnpike coppers. give em hades. bob f |
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| Author: | wjajr [ Tue Dec 15, 2015 6:28 am ] |
| Post subject: | |
Quote: i would go further and would like to see a 318 in an f or a body with the 2.45 axle and manual trans.
Many moons ago we had a 1976 Cordoba, 400 4v lean burn, 727 3 speed fresh off the showroom floor that I believe had a 2.45 rear gear. Any kid on a bicycle could beat that tank out of a light and be three car lengths down the road before that 400 could get into its torque curve; but it did make a real nice deep dulcet note on its way to takeoff. And, it could break the national double nickel speed limit handily in first gear; 93 mph was WOT shift point into third. That peg-leg couldn't spin a tire on wet pavement. However once that thing got to 35 mph in first gear, the front end would heave up like an old Crist craft trying to plane out, and it was off to the races with that 4v just a howling. Fuel consumption of 19 mpg heading west, and 19.5 mpg heading east during several trips between Maine & Chicago. Why the difference; probably tail wind blowing east.I can see where a six would be hobbled around town with a high geared rear, and OD. I remember riding in a friend's OD 4 speed Aspen, and it was always lugging in or out of OD on two lane eastern Mass. roads. At 55 mph it was a slug in OD. |
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| Author: | GTS225 [ Tue Dec 15, 2015 3:34 pm ] |
| Post subject: | |
Hmmmm. Plymouth Arrow, 170 inch motor, OD trans, and a 2:45 geared rear. Sounds like a Bonneville package. Wait....the engine transplant would through it into a modified class. Maybe a little 65-66 fastback Valiant or Barracuda. Anybody know what Wilford Day's drivetrain package was? Roger |
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| Author: | Dart270 [ Thu Dec 17, 2015 8:19 am ] |
| Post subject: | |
That package already exists and will be running at Bonneville this August (maybe Oct too). 66 B'cuda, 170, 4spd, 3.23 gears. Mid 140s is target. 2.45s would be low unless turbocharged. Lou |
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